I'm going for a GFA this year at Bournemouth sub 3:15. I ran the marathon last year and this race imo is best raced as a positive split because of the hill at mile 18. My plan is 1:35/1:39 (grit my teeth and hang on).
The wind will play a massive factor as the prom is so exposed (regular training run). The first half of the race is net downhill so that is the quick part of the race. Look at the marathon results for last year and you'll see a 3/4 minute positive split in almost all the runners times. I promise you the hill at mile 18 would be hard at any point of the race.